Process for coating a substrate, plant for implementing the process and feeder for feeding such a plant with metal

ABSTRACT

The invention relates to a coating process for coating at least one side of a running substrate, by vacuum evaporation, with a layer of a sublimable metal or metal alloy, in which said metal or metal alloy is positioned so as to face said side of the substrate in the form of at least two ingots placed in contact with one another, that surface of said ingots facing said side of the substrate being kept parallel to the substrate and at a constant distance from the latter during coating, and also to a coating plant for implementing the process and to a feeder ( 1 ) for supply

The present invention relates to a process for coating a running substrate, more particularly for coating steel strip with layers based on metallic elements such as, for example, magnesium, but without being in any way restricted thereto.

Various processes are known for depositing, on a running substrate, such as a steel strip, metallic coatings consisting of a layer of metal, or several successive layers of different metals, or else metal alloys. Among these processes, mention may be made of hot-dip galvanizing and electrodeposition, or indeed the various vacuum deposition (magnetron sputtering, Joule evaporation, electron bombardment and SIP (self-induced plasma)) processes.

Vacuum deposition processes have the advantage of being environmentally friendly and of enabling virtually all known elements, but also alloys, to be deposited. When it is desired for a metallic layer to be continuously deposited on a running substrate, the problem of how to feed the deposition chamber with the metal to be deposited then arises.

A first type of coating plant is known in which the metal to be deposited is kept in liquid form by being melted in a furnace before being conveyed to the deposition zone, for example by means of a pump or else by the barometer principle. However, this type of plant is not suitable for depositing metallic elements that sublime, i.e. those which pass directly from the solid phase to the vapour phase.

A second type of coating plant is known in which the metal to be deposited is in solid form, such as for example in the form of wires, which are introduced in a regular manner therein, or else in the form of granules, which are placed inside an inert graphite crucible. These plants are able to deposit metallic elements that sublime, but the deposition process is unstable, resulting in non-uniform coating thicknesses over the course of time, and is limited in terms of heating power, preventing sufficiently high deposition rates from being achieved.

The object of the present invention is therefore to remedy the drawbacks of the processes of the prior art by providing a process for coating a running substrate with a sublimable metal or metal alloy that allows stable operation over time at a high deposition rate.

For this purpose, a first subject of the present invention is a coating process for coating at least one side of a running substrate, by vacuum evaporation, with a layer of a sublimable metal or metal alloy, in which said metal or metal alloy is positioned so as to face said side of the substrate in the form of at least two ingots placed in contact with one another, that surface of said ingots facing said side of the substrate being kept parallel to the substrate and at a constant distance from the latter during coating.

The process according to the invention may also include various features, taken individually or in combination:

-   -   the ingots of a sublimable metal or metal alloy may be moved         simultaneously, either continuously or sequentially, so as to         keep their surfaces facing the substrate parallel to and at a         constant distance from the latter;     -   the ingots of a sublimable metal or metal alloy may be moved         simultaneously by translation, the opposite surface of the         ingots from that facing the substrate being in contact with an         inclined plane;     -   the ingots may be moved simultaneously by translation in a plane         parallel to the plane in which the substrate runs and in a         direction perpendicular to the direction in which the substrate         runs, the opposite surface of the ingots from that facing the         substrate being in contact with an inclined plane;     -   the ingots may be moved simultaneously by translation in a plane         parallel to the plane in which the substrate runs and in a         direction parallel to the direction in which the substrate runs,         the opposite surface of the ingots from that facing the         substrate being in contact with an inclined plane;     -   the substrate may run vertically, the ingots being stacked one         on top of another;     -   the substrate may be coated by vacuum evaporation on both its         sides with a layer of a sublimable metal or metal alloy, the         metal or metal alloy being positioned so as to face each side of         the substrate in the form of at least two ingots placed in         contact with one another, that surface of the ingots facing each         side of the substrate being kept parallel to and at a constant         distance from the side of the substrate during coating;     -   the metal or metal alloy may be the same or different for each         side of the substrate;     -   the vacuum evaporation process may be deposition by         plasma-enhanced evaporation, such as deposition by SIP         (self-induced plasma) evaporation;     -   the metal or metal alloy may be chosen from zinc, magnesium,         chromium, manganese, silicon and alloys thereof and is         preferably magnesium or one of its alloys;     -   the deposition by vacuum evaporation may be carried out in a         reactive atmosphere; and     -   the running substrate may be a steel strip, possibly already         coated beforehand, and preferably a steel strip which has been         coated beforehand with zinc or a zinc alloy and on which a layer         of magnesium or magnesium alloy is deposited.

A second subject of the invention is a coating plant for continuously coating a substrate S on at least one of its sides with a layer of a sublimable metal or metal alloy, comprising a vacuum chamber containing:

-   -   a vacuum evaporation coater;     -   means for making said substrate S run through the coater; and     -   a feeder 1, 11, 21 for feeding the coater with a metal or metal         alloy, said metal or metal alloy being in the form of ingots L1,         . . . , Ln, L′1, . . . , L′n and comprising means for keeping         said ingots L1, . . . , Ln, L′1, . . . , L′n in contact with one         another and for keeping that surface of the ingots L1, . . . ,         Ln, L′1, . . . , L′n facing the side of the substrate S to be         coated parallel to and at a constant distance from the substrate         S.

The plant according to the invention may also comprise the following embodiments, taken individually or in combination:

-   -   the feeder 1, 11, 21 may comprise means for simultaneously         moving the ingots L1, . . . , Ln, L′1, . . . , Ln sequentially         or continuously so as to keep their surfaces facing the         substrate S parallel to and at a constant distance from the         latter;     -   the feeder 11 may comprise at least one inclined plane 2, 2′         with which the ingots L1, . . . , Ln, L′1, . . . , L′n are in         contact via their side opposite that facing the substrate S, the         means for moving the ingots L1, . . . , Ln, L′1, . . . , L′n         enabling them to be moved by translation in a plane parallel to         the plane in which the substrate S runs and in a direction         perpendicular to the direction in which the substrate S runs,         and the inclination of the inclined plane 2, 2′ increasing in         the direction of movement of the ingots L1, . . . , Ln, L′1, . .         . , L′n;     -   the means for moving the ingots L1, . . . , Ln, L′1, . . . , L′n         may consist of at least one piston 3, 3′ acting on a first ingot         L1, L′1 in contact with a first end of the inclined plane 2, 2′,         and extending transversely relative to the substrate S, the         first ingot L1, L′1 acting in turn on the ingots L2, . . . , Ln,         L′2, . . . , L′n preceding it on said inclined plane 2, 2′ as         far as its second end;     -   the plant may have a first inclined plane 2 provided with ingots         L1, . . . , Ln and with a first piston 3 acting on the first         ingot L1 in contact with the first end of the first inclined         plane 2 and a second inclined plane 2′ provided with ingots L′1,         . . . , L′n and with a second piston 3′ acting on the first         ingot L′1 in contact with the first end of the second inclined         plane 3′, it being possible for said pistons 3, 3′ to act in the         same direction or in opposed directions;     -   the plant may comprise two tanks 4 for recovering, by gravity,         the spent ingots U, said tanks being placed beneath each second         end of the inclined planes 2, 2′;     -   the feeder 11, 21 may have at least one inclined plane 12, 22         with which the ingots L1, . . . , Ln are in contact via their         side opposite that facing the substrate S, the means for moving         the ingots enabling them to be moved by translation in a plane         parallel to the plane in which the substrate S runs and in a         direction parallel to the direction in which the substrate S         runs, and the inclination of the inclined plane 12, 22         increasing in the direction of movement of the ingots L1, . . .         , Ln;     -   the means for moving the ingots L1, . . . , Ln may consist of at         least one piston 13, 23 acting on a first ingot L1 in contact         with a first end of the inclined plane 12, 22, and extending         longitudinally relative to the substrate S, the first ingot L1         acting in turn on the ingots L2, . . . , Ln preceding it on the         inclined plane 12, 22 as far as its second end;     -   the plant may comprise a tank for recovering, by gravity, the         spent ingots, said tank being placed beneath the second end of         the inclined plane 12, 22;     -   the substrate S may run vertically, the feeder 21 comprising at         least one vertical plate 24 on which the ingots L1, . . . , Ln         are stacked, said plate being in contact with at least one         vertical piston 23;     -   the plant may comprise a feeder 1, 11, 21 facing each side of         the substrate S, it being possible for each feeder 1, 11, 21 to         contain an identical or different metal or metal alloy, and a         vacuum evaporator facing each side of the substrate S, the         assembly being placed within the same vacuum chamber;     -   the plant may include means for introducing a reactive         atmosphere into the vacuum chamber;     -   the vacuum evaporator(s) may be plasma-enhanced evaporation         deposition devices, such as a device for deposition by         self-induced plasma (SIP) evaporation; and     -   the ingots L1, . . . , Ln, L′1, . . . , L′n of a metal or metal         alloy may be chosen from zinc, magnesium, chromium, manganese,         silicon and alloys thereof.

A third subject of the invention is a feeder 1, 11, 21 for feeding a vacuum coating plant as defined above with a metal or metal alloy.

Other features and advantages of the invention will become apparent on reading the following description, given solely by way of example and with reference to the appended drawings which represent:

FIG. 1: a sectional view of a metal ingot employed by a process is according to the prior art;

FIG. 2: a perspective view of a first embodiment of a plant according to the invention;

FIG. 3: a perspective view of a second embodiment of a plant according to the invention; and

FIG. 4: a perspective view of a third embodiment of a plant according to the invention.

Within the context of the present invention, the term “evaporation process” is understood to mean any deposition process by evaporation at a pressure below atmospheric pressure. Preferably, the evaporation will be carried out by the SIP (self-induced plasma) process in which vacuum evaporation is combined with magnetron sputtering.

This process consists in creating a plasma between a substrate and a crucible containing the material to be deposited, in a gas for generating radicals and/or ions. Under normal operating conditions, these ions will be accelerated onto the surface of the material to be deposited on the substrate and tear off surface atoms, which are then deposited on the substrate. At the same time, the bombardment of the ions created in the plasma heats up the material to be deposited, enabling an evaporation process to added to the magnetron sputtering. The reader may refer in particular to patent EP 780 486 for more details about the implementation of this process.

The substrate to be coated moves through a vacuum chamber facing the crucible containing the material to be deposited. The crucible is negatively biased relative to the substrate, the latter preferably being earthed. An array of magnets positioned behind the crucible confines the plasma created therein. In order for the substrate to be coated to be positioned very precisely with respect to the crucible, the substrate is generally placed on a support roll, which may be rotated about its axis. However, this type of roll is unnecessary when substrates in rigid plate form, such as thick metal plates or glass plates, are treated.

The process according to the invention therefore consists in depositing a layer of a metal or metal alloy on a running substrate.

This process applies more particularly, but not solely, to the treatment of steel strip, preferably strip coated with zinc or a zinc alloy. The term “zinc alloy” is understood to mean any compound comprising at least 50% zinc and able to contain, for example, aluminium, iron, silicon, etc.

This prior coating may be obtained by any known galvanizing process, whether for example hot-dip galvanizing, electrodeposition or deposition by vacuum evaporation. However, vacuum deposition processes are preferred.

The coating deposited within the context of the present invention is a metallic coating based on elements that can sublime during their deposition by vacuum evaporation. In particular, this covers elements such as zinc, magnesium, chromium, manganese and silicon, for example. It is particularly preferable to deposit magnesium on a strip precoated with zinc after which a diffusion treatment may be carried out by any suitable means, so as in the end to obtain a Zn—Mg coating having, in particular, a high performance in terms of corrosion resistance.

The present inventors firstly conducted evaporation trials on a static bulk magnesium ingot facing a steel strip running through a SIP vacuum deposition plant.

After a certain operating time, it was observed that the coating deposited did not have a uniform thickness and that the deposition rate was relatively low. The deposition therefore had to be interrupted, making it possible to observe the state of the ingot, a representation of which is reproduced in FIG. 1.

It may be seen that the wear of the ingot is very irregular and to particularly accentuated in line with the high-magnetic-field zone. Without wishing to be tied to one particular theory, the present inventors consider that the instability of the deposition process is directly due to the irregular wear of the ingot.

To stabilize the process, the inventors therefore split the bulk ingot into at least two ingots and kept the top sides of these ingots parallel to and at a constant distance from the substrate to be coated, continuously or sequentially compensating for the wear due to evaporation.

For this purpose, a first coating plant according to the invention using the SIP process was developed, this being partly reproduced in FIG. 2 in which a feeder 1 may be seen.

The feeder is placed beneath the substrate to be coated (not shown) which runs horizontally above the system of magnets A for confining the magnetic field, these being placed in a water box. A counterelectrode (not shown) is placed beneath the feeder 1 and a plasma is created by discharge between the counterelectrode/magnets assembly and the steel strip. To make the system easier to understand, the preferential erosion zone has been shown by means of a circuit T, which represents the zone where the magnetic field is intense.

The feeder 1 comprises a first inclined plane 2, the inclination of which increases from left to right. This inclined plane may be made of any appropriate material, provided that it is not liable to be sputtered during the operation, which would contaminate the coating obtained. This first inclined plane 2 could for example be made of tungsten.

A series of n ingots L1 to Ln is placed on this inclined plane 2, these being in contact with one another and their heights decreasing from left to right. The inclination of the inclined plane 2 is adapted so as to compensate for the wear of the ingots L1 to Ln, in such a way that the top sides of the ingots L1 to Ln remain mutually parallel and parallel to the substrate to be coated that is running above the device 1, perpendicular to the inclined plane 2. A constant distance is thus maintained between the magnets and the top side of the ingots, and also a constant distance between the top side of the ingots and that side of the substrate to be coated. The reason for this is that, to obtain the most homogeneous plasma possible, it is important for the distance between electrodes (consisting here of the ingots on the one hand and the substrate on the other) to be as constant as possible. It is also just as important for the distance between the magnets of the magnetron and the top side of the ingots to remain constant. If these conditions are not met, owing to consumption of the ingots, at any point on their top side, the plasma will be locally intensified or diminished, generating instabilities in this plasma, and thus instabilities in the evaporation.

The use of an inclined plane 2 thus makes it possible to obtain a very stable plasma at every point in the evaporation zone.

Provided on either side of the ingots L1 to Ln are two lateral tungsten guides 6 that keep these ingots L1 to Ln properly aligned.

Placed to the left of the first ingot L1 is a piston 3 that acts on this first ingot L1 so as to move it translationally to the right, while still being guided by the inclined plane 2 and the lateral guide 6. The movement of the ingot L1 shifts, in a cascade fashion, all the ingots placed on the inclined plane 2 until the end ingot Ln drops under gravity into a recovery tank 4 for collecting the spent ingots, which may be melted and reused.

When the end of the piston 3 which is the first end of the inclined plane 2 it is at the end of its travel, it is then actuated in the opposite direction. Secondly, a vertical piston 5 acting on a support plate, supporting a series of p fresh ingots R1 to Rp, is actuated upwards so as to present a new ingot level with the first end of the inclined plane 2. The piston 3 is then brought into contact with the lateral side of the ingot R1, which is pressed against the first ingot L1 in contact with the inclined plane 2.

Thus, it may be seen that the feeder may be supplied with ingots continuously, without interrupting the process, and keeping the surface of the ingots in use both flat and parallel to the substrate to be coated thanks to the inclined plane 2 and to the regular movement imposed by the piston 3.

To cover the majority of the intense magnetic field zone T and therefore to optimize the deposition rate, a second feeder 1′ in every way identical to the feeder 1 is placed facing the second half of the zone T. Here, the piston 3′ moves the second series of n ingots L′1 to L′n from right to left, the inclined plane 2′ being of the opposite orientation to the inclined plane 2, but it would be quite possible to provide two feeders which are identical in all points for each half of the zone T.

It may be seen that, in this embodiment, it is possible to optimize the size of the ingots by determining their width depending on the width of the zone T.

A second embodiment, as shown in FIG. 3, shows a feeder 11 comprising, in a similar way to the first embodiment, an inclined plane 12 supporting a series of n ingots L1 to Ln extending transversely relative to the running substrate in a horizontal plane (not shown). The environment of the feeder 11 is identical to that described in the case of FIG. 2.

The ingot L1 is moved through the action of the pistons 13, which advance the ingots L1 to Ln on the inclined plane 12 until they drop, under gravity, into a recovery tank (not shown) placed beneath the second end of the inclined plane 12.

The system is recharged with ingots by means of a plate 14 moved by two pistons 15, which plate supports a stack of p ingots R1 to Rp and operates in the same way as the device corresponding to FIG. 2. Provided on both sides of the ingots L1 to Ln are two lateral tungsten guides 16 which keep these ingots L1 to Ln properly aligned.

It may also be seen that this embodiment of the plant according to the invention allows easy adaptation to various widths of substrates to be coated since all that is required is to modify the width of the ingots and the spacing of the parts 16 in order to obtain a feeder having precisely the width necessary for the coating in progress.

A third embodiment, as shown in FIG. 4, shows a feeder 21 comprising, in a similar manner to the first embodiment, two inclined planes 22 supporting a series of n ingots L1 to Ln extending transversely relative to the substrate S running in a vertical plane. These inclined planes 22 also have lateral cheek plates which ensure correct alignment of the ingots.

The ingot L1 is moved through the action of two vertical pistons 23 on a vertical plate 24, thereby advancing the ingots L1 to Ln along the inclined planes 22.

When the top ingot Ln arrives beyond the end of the inclined planes 22, a horizontal piston 25 is actuated laterally against the side of this ingot, which can thus be removed sideways.

This embodiment allows the substrate to be easily coated in a vertical position. This position also makes it possible for a two-side coating to be very easily applied by placing a feeder according to the invention on each side of the substrate, while still being placed within the same reduced-pressure chamber.

Trials

Trials were carried out using an arrangement in accordance with the first embodiment and an SIP evaporation device. Pure zinc ingots or pure magnesium ingots 4 cm in thickness and 10 cm in width were used to coat steel strips varying in width between 50 and 200 cm. Each steel strip ran over a support roll at 100 m/min. The ingot evaporation rate was also varied.

The distance between the top side of the ingots and the steel strips to be coated was kept at 5 cm and the chamber opening, corresponding to the deposition zone in the direction in which the strip runs, was set to 40 cm. In all the trials carried out, the ingot run speed necessary for obtaining a coating thickness of around 1.5 μm was determined.

The results are given in the following three tables:

Coating material Zn Strip width (cm) 50 100 150 200 SIP module width (cm) 70 120 170 220 Evaporation rate (g/cm²/s) 0.01 0.01 0.01 0.01 Ingot run speed (cm/min) 2 3.4 4.8 6.2 Coating material Zn Strip width (cm) 50 100 150 200 SIP module width (cm) 70 120 170 220 Evaporation rate (g/cm²/s) 0.02 0.02 0.02 0.02 Ingot run speed (cm/min) 4 6.8 9.6 12.4 Coating material Mg Strip width (cm) 50 100 150 200 SIP module width (cm) 70 120 170 220 Evaporation rate (g/cm²/s) 0.002 0.002 0.002 0.002 Ingot run speed (cm/min) 1.6 2.8 4 5.2

These show that the ingot run speed essentially depends on the width of the strip to be coated and on the rate of evaporation of the coating material.

Similar results were obtained using arrangements in accordance with the second and third embodiments.

More generally, it was found that an ingot run speed of between 1 and 15 cm/min allowed the desired coating thickness targets to be achieved. If it is desired to achieve greater coating thicknesses, all that is then required is to pass the substrate through a series of coaters. Thus, to obtain a zinc thickness of around 7.5 μm under the evaporation conditions indicated in the above tables, five coaters would be required.

Whatever the embodiment adopted, the invention also has the advantage of not requiring the use of graphite crucibles, thereby making it possible for deposition to take place in a reactive atmosphere. This makes it possible in particular to deposit, for example, metal oxides, nitrides, sulphides and fluorides, with high deposition rates.

As was seen over the course of the description of a few preferred embodiments of the invention, the coating may especially be carried out when the substrate runs either horizontally or vertically. It goes without saying that the coating may also be carried out in any position of the substrate that would be intermediate between horizontal and vertical. 

1. A coating process for coating at least one side of a running substrate comprising vacuum evaporating a layer of a sublimable metal or metal alloy, in which said metal or metal alloy is in the form of at least two ingots placed in contact with each other, is positioned so as to face said side of the substrate, and the surface of said ingots facing said side of the substrate is kept parallel to and at a constant distance from the substrate during coating.
 2. The coating process according to claim 1, in which said ingots of a sublimable metal or metal alloy are moved simultaneously, either continuously or sequentially, so as to keep their surfaces facing the substrate parallel to and at a constant distance from the substrate.
 3. The coating process according to claim 2, in which said ingots of a sublimable metal or metal alloy are moved simultaneously by translation, wherein the opposite surface of the ingots from that facing the substrate is in contact with an inclined plane.
 4. The coating process according to claim 3, in which said ingots are moved simultaneously by translation in a plane parallel to the plane in which the substrate runs and in a direction perpendicular to the direction in which the substrate runs, wherein the opposite surface of the ingots from that facing the substrate is in contact with said inclined plane.
 5. The coating process according to claim 3, in which said ingots are moved simultaneously by translation in a plane parallel to the plane in which the substrate runs and in a direction parallel to the direction in which the substrate runs, wherein the opposite surface of the ingots from that facing the substrate is in contact with said inclined plane.
 6. The coating process according to claim 1, in which said substrate runs vertically, said ingots being stacked one on top of another.
 7. The coating process according to claim 1, in which said substrate is coated by vacuum evaporation on both its sides by a layer of a sublimable metal or metal alloy, wherein at least two ingots of said metal or metal alloy are placed in contact with each other and positioned so as to face each side of the substrate, and that surface of said ingots facing each side of the substrate is kept parallel to and at a constant distance from said side of the substrate during coating.
 8. The coating process according to claim 7, in which said metal or metal alloy is the same for each side of the substrate.
 9. The coating process according to claim 7, in which said metal or metal alloy is different for each side of the substrate.
 10. The coating process according to claim 1, in which the vacuum evaporation process is deposition by plasma-enhanced evaporation.
 11. The coating process according to claim 1, in which said metal or metal alloy is chosen from zinc, magnesium, chromium, manganese, silicon and alloys thereof.
 12. The process according to claim 11, in which said metal or metal alloy is magnesium or alloys thereof.
 13. The process according to claim 1, in which the deposition by vacuum evaporation is carried out in a reactive atmosphere.
 14. The process according to claim 1, in which the running substrate is a steel strip.
 15. The process according to claim 14, in which the running substrate is a steel strip which has been coated beforehand with zinc or a zinc alloy and on which a layer of magnesium or a magnesium alloy is deposited.
 16. A coating plant for continuously coating a substrate on at least one of its sides with a layer of a sublimable metal or metal alloy, comprising a vacuum chamber containing: a vacuum evaporation coater; means for making said substrate run through the coater; and a feeder for feeding the coater with a metal or metal alloy, said metal or metal alloy being in the form of ingots and comprising means for keeping said ingots in contact with one another and for keeping that surface of said ingots facing the side of the substrate to be coated parallel to and at a constant distance from said substrate.
 17. The coating plant according to claim 16, in which said feeder comprises means for simultaneously moving said ingots sequentially or continuously so as to keep their surfaces facing the substrate parallel to and at a constant distance from the latter.
 18. The plant according to claim 17, in which said feeder comprises at least one inclined plane with which said ingots are in contact via their side opposite that facing said substrate, said means for moving the ingots enabling them to be moved by translation in a plane parallel to the plane in which the substrate runs and in a direction perpendicular to the direction in which the substrate runs, and the inclination of said inclined plane increasing in the direction of movement of said ingots.
 19. The plant according to claim 18, in which said means for moving the ingots consist of at least one piston acting on a first ingot in contact with a first end of said inclined plane, and extending transversely relative to the substrate, said first ingot acting in turn on the ingots preceding it on said inclined plane as far as its second end.
 20. The plant according to claim 19, having a first inclined plane provided with ingots and with a first piston acting on the first ingot in contact with the first end of said first inclined plane and a second inclined plane provided with ingots and with a second piston acting on the first ingot in contact with the first end of said second inclined plane, wherein said pistons act in the same direction or in opposed directions.
 21. The plant according to claim 20, comprising two tanks for recovering, by gravity, the spent ingots, said tanks being placed beneath each second end of said inclined planes.
 22. The plant according to claim 17, in which said feeder has at least one inclined plane with which said ingots are in contact via their side opposite that facing said substrate, said means for moving the ingots enabling them to be moved by translation in a plane parallel to the plane in which the substrate runs and in a direction parallel to the direction in which the substrate runs, and the inclination of said inclined plane increasing in the direction of movement of said ingots run.
 23. The plant according to claim 22, in which said means for moving the ingots consist of at least one piston acting on a first ingot in contact with a first end of said inclined plane, and extending longitudinally relative to the substrate, said first ingot acting in turn on the ingots preceding it on said inclined plane as far as its second end.
 24. The plant according to claim 23, comprising a tank for recovering, by gravity, the spent ingots, said tank being placed beneath said second end of the inclined plane.
 25. The plant according to claim 22, in which the substrate runs vertically, said feeder comprising at least one vertical plate on which said ingots are stacked, said plate being in contact with at least one vertical piston.
 26. The plant according to claim 16, comprising a feeder facing each side of said substrate, it being possible for each feeder to contain an identical or different metal or metal alloy, and a vacuum evaporator facing each side of said substrate, the assembly being placed within the same vacuum chamber.
 27. The plant according to claim 16, comprising means for introducing a reactive atmosphere into said vacuum chamber.
 28. The plant according to claim 16, in which said vacuum evaporator(s) are plasma-enhanced evaporation deposition devices.
 29. The plant according to claim 16, in which said ingots of a metal or metal alloy are chosen from zinc, magnesium, chromium, manganese, silicon and alloys thereof.
 30. A feeder for feeding a vacuum coating plant, as defined in claim 16, with a metal or metal alloy. 